A microstrip antenna is a small-sized light-weight antenna that uses an MSL (microstrip line) formed on a dielectric substrate to transceive radio waves in a microwave or milliwave band, and used as a surveillance radar antenna or a communication antenna. For example, an MSL is configured to include a substantially linear feed line, a plurality of radiating elements arranged along the feed line, and a ground layer formed through a dielectric layer.
A conventional microstrip antenna is a planar antenna in which a radiating pattern and a feeding point constituting an MSL are formed on a front surface of a dielectric substrate and a ground layer is formed on a back surface side of the dielectric substrate, and can radiate electromagnetic waves only in one direction intersecting with the dielectric substrate (e.g., Patent Literature 1 (JP-A-2013-31064)). For this reason, in order to radiate electromagnetic waves in two or more different directions, it is necessary to arrange a plurality of microstrip antennas in mutually different directions, and feed high frequency signals to the microstrip antennas.
That is, in the case of attempting to radiate the electromagnetic waves in the two or more directions, it is necessary to fabricate a plurality of dielectric substrates, which gives rise to a problem of increased manufacturing costs. Also, in the case of distributing the high frequency signals to the respective dielectric substrates, and then feeding the high frequency signals to the respective microstrip antennas, there is a problem of a complicated configuration of transmission lines that connect a high frequency circuit and the microstrip antennas to each other.
On the other hand, in the case of distributing the high frequency signals on any of the dielectric substrates, and then feeding the high frequency signals to the respective microstrip antennas, MSLs should be connected between the dielectric substrates, and therefore connectors for MSL connection should be separately provided. For this reason, there are problems of increased manufacturing costs and also large power loss.